RAM has also been getting cheaper over the years (especially if you factor in price vs. performance), but we still want to get the most performance out of our memory as possible. You can purchase a "budget" set of RAM, but you are almost guaranteed to have no overclocking headroom. Better (and generally more expensive) memory runs at faster timings (4-4-4-12 instead of the standard-5-5-5-15).
A-Data has released their Vitesta PC2-8000 RAM, which is technically a DDR-800 set, but with a guaranteed overclock to DDR-1000 Speeds. This overclock translates into a 25% performance increase (8GB / second vs DDR2-800's 6.4GB /second). This also means that you can re-use this memory when you upgrade your motherboard to one that supports a fast 1GHz bus.